class_docstr: Describes how to name items that are involved in a MetricFlow query.
  
  Most useful for group-by-items as there are different ways to name them like "user__country"
  or "TimeDimension('metric_time', 'DAY')".
docstr: Following this scheme, return the string that can be used as an input that would specify the given spec.
  
  This is used to generate suggestions from available group-by-items if the user specifies a group-by-item that is
  invalid.
  
  If this scheme cannot accommodate the spec, return None. This is needed to handle unsupported cases in
  DunderNamingScheme, such as DatePart, but naming schemes should otherwise be complete.
docstr_tok: ["Following","this","scheme",",","return","the","string","that","can","be","used","as","an","input","that","would","specify","the","given","spec",".","This","is","used","to","generate","suggestions","from","available","group-by-items","if","the","user","specifies","a","group-by-item","that","is","invalid",".","If","this","scheme","can","not","accommodate","the","spec",",","return","None",".","This","is","needed","to","handle","unsupported","cases","in","DunderNamingScheme",",","such","as","DatePart",",","but","naming","schemes","should","otherwise","be","complete","."]
code: def input_str(self, instance_spec: InstanceSpec) -> Optional[str]:
      """Following this scheme, return the string that can be used as an input that would specify the given spec.
  
      This is used to generate suggestions from available group-by-items if the user specifies a group-by-item that is
      invalid.
  
      If this scheme cannot accommodate the spec, return None. This is needed to handle unsupported cases in
      DunderNamingScheme, such as DatePart, but naming schemes should otherwise be complete.
      """
      pass
  
file_path: metricflow/metricflow/naming/naming_scheme.py
imports: from __future__ import annotations
  from abc import ABC, abstractmethod
  from typing import Optional
  from metricflow.specs.patterns.spec_pattern import SpecPattern
  from metricflow.specs.specs import InstanceSpec
label_desc: Use image node_id 1 for calling the QueryItemNamingScheme obj's underlying member method code with example usage: obj.input_str(instance_spec) without return types